The instant invention relates to a graft polymer with ethylenically unsaturated, crosslinkable lateral chains and to a photocurable mixture, comprising said graft polymer and a photosensitive substance, which can be developed with aqueous solutions. The mixture is suited for the production of photosensitive recording materials, in particular planographic printing plates and photoresists.
Photosensitive mixtures comprising polyvinyl alcohols with photocrosslinkable side groups are known. U.S. Pat. No. 4,272,620 discloses a polyvinyl alcohol with lateral styrylpyridinium groups, which is distinguished by a high solubility in water and high photosensitivity. This alcohol is suited for protective coatings and screen printing stencils. U.S. Pat. No. 4,339,524 describes photosensitive resins which are suitable, in particular, for the production of luminescent screens or fluorescent screens of cathode ray tubes. The compounds are partially saponified polyvinyl acetates which in addition to acetal-type-bonded stilbazolium groups (=styrylpyridinium groups) carry ordinary acetal groups. From EP-A 0,130,804 a photosensitive mixture is known which contains a water-soluble saponified polyvinyl acetate with styrylpyridinium groups or styrylquinolinium groups, a water-dispersible polymer, a polymerizable unsaturated compound and a photoinitiator. The components are employed in the form of aqueous emulsions or dispersions and are suited for the production of printing plates, especially of screen printing stencils. EP-A 0,025,210 is also directed to a photosensitive mixture which contains a polyvinyl alcohol reacted with styrylpyridinium or styrylquinolinium groups and which is particularly suited for the production of screen printing stencils.
The resins described in the above publications are distinguished by high photosensitivity. They suffer, however, from the drawback that due to their low resistance to water even the hardened layer areas swell when development is performed with aqueous solutions, which seriously impairs image resolution.
This drawback cannot be avoided by an increased crosslinking density, for the incorporation of additional styrylpyridinium or styrylquinolinium groups on the one hand results in an increase in viscosity to the extent that coating of aluminum foils, for example, is no longer possible. On the other hand, the resistance to water is not sufficiently increased. This may be attributable to the presence of quaternary ammonium salt groups or to the fact that the degree of photodimerization cannot be arbitrarily increased by increasing the number of possible crosslinking points.
In DE-A 37 32 089 graft polymers are described, which comprise a polyurethane as the graft backbone and grafted-on vinyl ester units, which are at least partially saponified to give vinyl alcohol units. The polymers are suitable as binders for pigments; for preparing printing inks, thermoplastic adhesives and solvent-containing adhesives; as constituents of varnishes or coatings for fibers, films and metals, and for thermoplastic shaped articles.
Prior German Patent Application P 38 35 840.9 describes graft polymers which are obtained from the graft polymers described in DE-A 37 32 089 by acetalization with saturated aliphatic or aromatic aldehydes.
Prior German Patent Application P 39 20 229.1 describes photopolymerizable mixtures in which the graft polyvinyl acetals described in P 38 35 840.9 are contained as binders.
Prior German Patent Application P 39 24 811.9 describes photocurable graft polymers which are obtained from the polymers according to DE-A 37 32 089 by reacting them with activated derivatives of compounds having terminal vinyl or vinylidene groups, for example, derivatives of acrylic or methacrylic acid. These photocurable polymers are used in the production of printing plates or photoresists, in combination with photoinitiators and, optionally, free radically polymerizable low molecular weight compounds.